770
ShortCommunications
[Auk,Vol. 104
ProlongedSperm StorageDuration in DomesticatedCanaries
T. R. BIRKHEAD
Zoology
Department,
TheUniversity,
Sheffield
S102TN, UnitedKingdom
Relative to most mammals, female birds can retain
their fertility for a considerabletime after mating and
separationfrom the male (Lake 1975).Maximum sperm
storagedurations range from about 6 days in Ringed
Turtle-Doves (Streptopelia
risoria),16 days in ducks,
and 35 days in chickens to 72 days in turkeys (see
Birkhead 1987 for a review). No published information is available on the duration of sperm storagein
passerines.Here I report maximum spermstorageval-
weekspreviously.The other 8 birdsin the aviary were
subsequentlypaired and confirmed to be females.Estimated sperm storageduration was 35 days.
(4) A female canarywas paired to a male European
Goldfinch (C. carduelis),and the male removed once
the clutch was complete.A single goldfinch mule was
reared:this took 42 days (14 days of incubation and
28 daysto rear the chick).The femalecanarywasthen
paired immediately with a male siskin, and within a
ues for female domesticated Common Canaries (Ser-
week a clutch had been laid. One chick was reared
inus canaria).
from this clutch, but this was alsoa goldfinch rather
than a siskin mule. Estimatedsperm storageduration
was 49 days.
(5 and 6) The situation was identical to that in (2)
above, except that after the second brood had been
I collecteddata from a questionnaireto breedersof
canariesand "mules" (i.e. hybrids between a British
finch male x canary female). Six independent instanceswere reported; in each case female canaries
laid fertile eggsseveraldaysor weeksafter separation
from the males. Routinely, some breeders separate
the male and female after the clutch has been laid,
leaving the female to incubate and rear the young
alone (Carr 1959, Dodwell 1986). After the first brood
had been reared,somefemaleslaid fertile eggswithout being remated. Other instancesinvolved casesof
unexpectedpaternity when femaleshad been paired
with males of two different finch speciesin succession. In each casedescribed below I give the most
conservativeestimate of the duration of sperm storage.
(1) A female canary was paired to a male Eurasian
reared and the chicks removed, the female laid a third
clutch without being remated. The entire third clutch
was fertile, but it is not known whether the eggs
hatched. Estimated sperm storage duration was 35
days for the secondclutch and 68 days for the third
clutch.
Although theseindividual values are conservative,
they are likely to lie near the extreme for canaries.
Nonetheless,the maximum value, 68 days, is similar
to the maximum record for any bird species:72 days
in domesticatedturkeys (Lorenz 1950) and 60 days in
Grey-facedPetrels(Pterodroma
macroptera,
Imber 1976;
see Perrins and Brooke 1976, Hatch 1987 for infor-
Linnet (Cardueliscannabina),but the linnet died before
any eggswere laid. Approximately 3 weeks later the
mation for other Procellariiformes).
Information on the duration of sperm storage is
female canarywaspaired to a male CommonRedpoll
(C.fiammea);they built a nestand a clutchwasstarted
after 7 days. Of the clutch of 4 eggs, 2 were fertile.
When the chicks fledged they were clearly linnet
rather than redpoll mules,i.e. the linnet had fertilized
the eggs,not the redpoll. Sperm storageduration was
estimatedat 28 days.
(2) A male and female canarywere separatedafter
egglaying and the femaleleft to incubate(13-14 days)
and rear the young alone. After the chickswere removed (aged 21 days), the female laid a secondclutch
"within days";one egg was fertile and subsequently
hatched. Estimated sperm storage duration was 35
days.
(3) Ten canaries,all thought to be female, were
maintained in an aviary over winter. In early February one bird (obviouslya male) was heard singing
essentialif one is to calculateaccuratelythe period
over which a female bird might be fertilized. In particular, it is important to know the timing and duration of this period to determine whether extrapair
copulationsoccurwhen they could fertilize eggs.Several workers, including me (Birkhead 1982), have assumed, in the absenceof data, that sperm storage
duration in passerinesis considerably less than the
values presented here suggest.
The adaptive significanceof the prolonged sperm
storage that occurs in some birds is poorly understood,but it may be important in speciesin which
females copulate infrequently but produce large
clutches(e.g. some Galliformes;see Birkhead et al.
1987)and in seabirds,where the femalemay be away
from the colony and her partner for extended periods
before laying (seeImber 1976,Hatch 1983). There is
no compellingreasonwhy canariesshould have pro-
and removed.
Four weeks
later one of the females
was paired to a male Eurasian Siskin (C. spinus)in a
separatecage;this pair built a nest and started to lay
within a week. From the clutchof 5 eggs3 were fertile
and proved to be canaries,not siskin mules. The female could have been fertilized only by the male
canary,which had been removed from the aviary 4
longed sperm storage.Wild canariesproduce clutches
of 4-5 eggs (Bannerman and Bannerman 1968), and
the male and the femaleare unlikely to be apart for
long periods.In all other carduelinefinchesthat have
been studied, and in domesticated
canaries, mate
guarding is well developed; the male remains with
October1987]
ShortCommunications
771
the female continuouslyuntil she startsto incubate --,
L. ATKIN,& A. P. MOLLER.1987. Copulation
behaviour in birds. Behaviour
101: 101-138.
(Tsuneki 1961;Newton 1972,pers.comm.).One possible explanation for the results on canariesis that CARR,V. A.V. 1959. Mule and hybrid birds.London,
selectivebreedingduringtheperiodof domestication
Cage Birds.
(ca.350yr; Dodwell 1986)hasproducedincidentally CLAYTON,
G.A. 1972. Effectsof selectionon reproa well-developedspermstorageability(Clayton1972,
duction in avian species.J. Reprod. Fert. Suppl.
15: 1-21.
Lake 1975). This idea is plausiblebecausebreeders
have undoubtedly selectedfor individuals that bred
DODWELL,
G.T. 1986. The completebookof canaries.
London, Merehurst Press.
successfully
in captivity,and prolongedspermstorage contributesto successfulbreeding. In addition, HATCrt,S. A. 1983. Mechanismand ecologicalsigspermstoragedurationsdiffer significantlybetween
nificanceof spermstoragein the Northern Fuldifferent strains of chickens selected for different traits
mar with reference
(TanejaandGowe1961),indicatingthatspermstorage
Auk 100: 593-600.
duration hasa geneticbasis.Another explanationfor
theseresultsis that they representa few very rare
occurrences
at the extreme
end of the distribution
of
spermstoragedurationin canaries.A systematicstudy
to its occurrence
in other birds.
1987. Copulationand mateguardingin the
Northern
Fulmar.
Auk
104: 450-461.
IMBER,M. J. 1976. Breeding biology of the GreyfacedPetrel Pterodroma
macroptera
gouldi.Ibis ! ! 8:
51-64.
of spermstoragein canariesand other passerines,
particularlywild species,might be interesting.
LAKE,P. E. 1975. Gameteproduction and the fertile
I am extremelygrateful to the individualswho pro-
videdinformationonwhichthisnoteisbased:J.Maylan, R. Moat, T. Roberts,J. Robson,K. Swarm, and A.
C. Wyatt. I also thank Drs. M. de L. Brooke, K. M.
period with particular reference to domesticated
birds. Syrup. Zool. Soc. London 35: 225-244.
LORENZ,
F.W. 1950. Onsetand durationof fertility
in turkeys.Poultry Sci. 29: 20-26.
Cheng,A. P. Moller, and I. Newton for commenting NEWTON, I. 1972. Finches. London, Collins.
on the manuscript.
PERRINS, C. M., & M. DE L. BROOKEß 1976.
Manx
Shearwatersin the Bay of Biscay.Bird Study 23:
295-299.
LITERATURE CITED
BANNERMAN,D. A., & W. M. BANNERMAN. 1968. Birds
TANEJA,
G. C., & R. S. GOWE.1961. Effectof varying
dosesof undiluted semenon fertility in the do-
of the Atlantic islands.Edinburgh.
BIRKHEAD,
T. g. 1982. Timing and durationof mate
guardingin MagpiesPicapica.Anita. Behav.30:
TSUNEKI,
K. 1961. Territory in flocksof the caged
277-283.
ß 1987. Behaviouralaspectsof sperm competition in birds. Adv. Stud. Behav.in press.
mestic fowl.
Nature
London
191: 828-829.
canaries,with special reference to its causation
and defence.JapaneseJ. Ecol. 11: 19-26.
Received
28 January1987,accepted
22 April 1987.
Energetic Consequencesof Sexual Size Dimorphism in
White
Ibises (Eudoclmus
albus)
KEITH L. BILDSTEIN
Departmentof Biology,WinthropCollege,RockHill, SouthCarolina29733USA, and
Belle W. BaruchInstitutefor Marine Biology,Universityof SouthCarolina,
Columbia, South Carolina 29208 USA
Sexual dimorphism is pronounced in White Ibises
(Eudocimus
albus):malesare heavier than females,and
they have substantiallylonger tarsi, bills, and wing
chords(Kushlan 1977a).Sexualsize dimorphismmay
result either from natural selectionacting to reduce
intersexualfood competition or to increaseclutch size
in females (cf. Carothers 1984), or from sexual selec-
tion acting to enhance the mating successof appropriately sized individuals. Kushlan (1977a)proposed
that the sizedimorphismhe reportedfor White Ibises
resulted from sexualselectionacting to increasebody
size and bill length in males.
Male ibisesuse their bills during courtship,when
males and females
intertwine
their
bills and necks
during pair formation(Palmer1962,Rudegeair1975),
and during copulation,when malesextend their bills
over femalesand engagein twig pulling (Rudegeair
1975).A larger bill and body in malesundoubtedly
is also important for intrasexual fighting during
courtship,mating,and nestbuilding,when malesfight
overmatesandattemptnest-sitetakeovers(Rudegeair
1975,Frederick 1986).Fighting ability in maleshas
alsobeen linked to increasedextrapaircopulationsin
this sometimespromiscuous
species(Frederick1985a).
Although female ibisesparticipatein aggressiveinteractionsat the colonysite,femaleaggression
is con-